Functional Roles of E3 Ubiquitin Ligases in Gastric Cancer (Review)

ONCOLOGY LETTERS 20: 22, 2020

Functional roles of E3 ubiquitin ligases in gastric cancer (Review)

MINGLIANG WANG1*, WEI DAI1*, ZHANGYAN KE2* and YONGXIANG LI1

Departments of 1General Surgery and 2Geriatric Medicine, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui 230032, P.R. China

Received August 30, 2019; Accepted April 29, 2020

DOI: 10.3892/ol.2020.11883

Abstract. To date, >650 E3 ubiquitin ligases have been Contents described in humans, including >600 really interesting new genes (RINGs), 28 homologous to E6‑associated protein 1. Introduction C‑terminus (HECTs) and several RING‑in‑between‑RINGs. 2. Classification of E3 ubiquitin ligases They are considered key regulators and therapeutic targets of 3. Structure and function of RING‑type E3 ligases in GC many types of human cancers, including gastric cancer (GC). 4. Structure and function of HECT‑type E3 ligases in GC Among them, some RING and HECT E3 ligases are closely 5. Therapeutics targeting E3 ligases in GC related to the proliferation, infiltration and prognosis of GC. 6. Conclusions and perspectives During the past few years, abnormal expressions and functions of many E3 ligases have been identified in GC. However, the 1. Introduction functional roles of E3 ligases in GC have not been fully eluci‑ dated. The present article focuses on the functional roles of E3 Gastric cancer (GC) is the fourth most commonly diagnosed ligases related to the proteasome in GC. In this comprehensive cancer and the third leading cause of cancer‑related mortality review, the latest research progress on E3 ligases involved in GC worldwide (1). The pathogenic mechanisms and progression and elaborate their structure, classification, functional roles and of GC are complex. Currently, well‑known pathogenic factors therapeutic value in GC was summarized. Finally, 30 E3 ligases include poor eating habits, chronic Helicobacter pylori that serve essential roles in regulating the development of GC infection and the misregulation of oncogenes or tumor were described. Some of these ligases may serve as oncogenes or suppressors (2). The 5‑year survival rate of patients with GC tumor suppressors in GC, whereas the pathological mechanism is only 27.4% in China (3). The poor prognosis of GC is due of others needs further study; for example, constitutive photo‑ to tumor invasion and metastasis (4,5), which are complex morphogenic 1. In conclusion, the present review demonstrated processes involving a series of cell biological regulations and that E3 ligases are crucial tumor regulatory factors and potential requiring multi‑step genetic mutations (6). The genes and their therapeutic targets in GC. Therefore, more studies should focus products involved in each step of tumor progression are poten‑ on the therapeutic targeting of E3 ligases in GC. tial prognostic markers and therapeutic targets. Among these biomarkers, E3 ligases play a crucial role in the proliferation, invasion and metastasis of GC (7). The ubiquitin‑proteasome system (UPS) is a common Correspondence to: Professor Yongxiang Li, Department of post‑translational modification pathway involved in the General Surgery, The First Affiliated Hospital of Anhui Medical regulation of cell survival and differentiation (8). The ubiqui‑ University, 218 Jixi Road, Hefei, Anhui 230032, P.R. China tination pathway is catalyzed by three types of key enzymes: E‑mail: [email protected] Ubiquitin‑activating enzyme (E1), ubiquitin‑conjugating enzyme (E2) and ubiquitin ligases (E3) (9). E3 ligase is the most * Contributed equally important component in the UPS owing to its specific ability to recognize target proteins and transfer ubiquitin to substrates Abbreviations: Cbl, casitas B lineage lymphoma; GC, gastric for degradation (9,10). To date, >650 E3 ubiquitin ligases have cancer; HECT, homologous to E6‑associated protein C‑terminus; NEDD, neural precursor cell expressed developmentally been described in humans, and they can be subdivided into downregulated protein; RBR, RING‑in‑between‑RING; RING, three different families: Homologous to E6‑associated protein really interesting new gene; RNF, RING finger domain; UPS, C‑terminus (HECT), really interesting new gene (RING) ubiquitin‑proteasome system and RING‑in‑between‑RING (RBR) E3 ligases (11,12). However, RBR E3 ligases, an emerging group of E3 ligases Key words: gastric cancer, E3 ligases, targeted therapy, ubiquitin, that feature with characteristics of RING and HECT, have signaling pathways not been discovered in GC (13). Hence, RING and HECT E3 ligases are dysregulated in GC cells. Owing to the notable role of E3 ligases on the ubiquitination of tumor‑associated 2 WANG et al: E3 UBIQUITIN LIGASES IN GASTRIC CANCER signaling molecules, such as the AKT pathway, targeting E3 previous studies have shown that RNF6 and RNF38 are over‑ ligases could be an efficient approach in cancer treatment (14). expressed in GC and regulate GC cell growth. Both RNF6 Recently, many new types of E3 ligases have been increasingly and RNF38 induce polyubiquitination of tyrosine‑protein detected in GC, such as RNF6 and RNF38 (15,16). Herein, a phosphatase non‑receptor type 6 and subsequently enhance comprehensive review of studies is presented to summarize STAT3 signaling, which promotes the proliferation of GC the latest progress and treatment prospects. cells (Fig. 1) (15,16). RNF26, which is located in the endoplasmic reticulum, is 2. Classification of E3 ubiquitin ligases a polypeptide of 433 amino acids with an N‑terminal leucine zipper domain and a C‑terminal RING finger domain (28,29). As aforementioned, only RING‑ and HECT‑type E3 ligases The expression level of RNF26 is upregulated in several types are involved in GC (Table Ⅰ). The RING family comprises of human cancer cell lines, including HL‑60, HeLa S3, SW480 >600 members (17). The RING finger domain is an important and MKN7 cells (28). As the substrate protein of RNF26, the component of RING‑type E3 ligases and can be sub‑divided mediator of interferon regulatory factor 3 can be ubiquitinated into two groups: Typical and atypical. The typical conserved and regulate the innate antiviral response (30). However, the region RING domain harbors a RING fold structure coupled functional mechanism of RNF26 in GC has not been fully with zinc ions. Another atypical type, called the U‑box elucidated. domain, possesses extremely similar RING folds but lacks Similar to RNF6, RNF26 and RNF38, RNF185 also acts as cysteine residues, which affects zinc ions coordination (18). an oncogene in GC, but with distinct subcellular localization Both RING and U‑box E3 ligases can function as monomers, and a distinct mechanism of action. RNF185 localizes to the homodimers, heterodimers or multiple subunits (17,19). The mitochondria, contains a C3HC4‑type RING domain and two cullin‑RING ligase (CRL) is a kind of multi‑subunit RING transmembrane domains (31). PRA1 family protein 3 (JWA) E3 ligase that can be further divided into the S phase kinase is a multifunctional cytoskeleton‑binding protein induced by associated protein 1 (SKP1)/cullin 1 (CUL1)/F‑box protein all‑trans retinoic acid. The function of JWA involves enhancing complex (SCF), CUL2‑elongin B/C‑VHL or SOCS proteins intracellular defenses against H2O2‑induced oxidative stress (CRL2), CUL3‑BTBs, CUL4‑DDB1‑DCAFs (CRL4), and reducing cell apoptosis (32). RN F185 can downregu‑ CUL5‑elonginB/C‑SOCS proteins, and the CUL7/F‑box/WD late the expression of JWA and promote GC cell migration repeat‑containing 8 (FBXW8) subfamily of E3 ligases (20,21). (Fig. 1) (33). Generally, higher expression of RNF185 is associ‑ HECTs, the second largest E3 ligase family in humans, ated with a worse prognosis of GC. comprises 28 members and can be categorized into three RNF43 and zinc/RING finger 3 (ZNRF3) are homologous subfamilies: Neural precursor cell expressed develop‑ proteins that have antagonistic effects in combination with mentally downregulated protein (NEDD)4 family, HECT leucine‑rich repeat‑containing G‑protein‑coupled receptor domain‑containing protein (HERC) family and ‘other’ 5 (Lgr5) (34). The Lgr5 protein, a member of the G‑protein HECT ligases (22). Studies to date have suggested that only coupled receptor family of proteins, was identified as a novel the NEDD4 family and a member of the Other HECT ligase gastrointestinal stem cell marker (35). Moreover, Lgr5‑positive families are related to GC. The NEDD4 subfamily is the most gastric stem cells are cancer‑initiating cells able to drive GC characteristic family, including nine members in humans: cell self‑renewal, which contributes to malignant progres‑ NEDD4‑1 (also known as NEDD4), NEDD4‑2, Itchy E3 sion (35‑37). RNF43 negatively regulates the Wnt/β‑catenin ubiquitin‑protein ligase, SMAD ubiquitin regulatory factor pathway by recognizing Lgr5 and markedly downregulating the (Smurf)1, Smurf2, WW domain‑containing E3 ubiquitin expression of Lgr5 protein (34). A previous study demonstrated protein ligase (WWP)1, WWP2, NEDD4‑like 1 (NEDL1) that ZNRF3 acts as a tumor suppressor by downregulating and NEDL2 (23). The Other HECT ligase family includes 13 the expression levels of β‑catenin and transcription factor members, and they all contain different domains in addition to 4 protein (38). RNF43/ZNRF3 mediates the ubiquitylation the HECT domain. of seven transmembrane domains of frizzled receptors and The structure and functional significance of RINGs in subsequently inhibits the proliferation of GC cells (39). A few GC will be described in the following paragraphs in the order large‑scale genomic analyses have reported RNF43 mutations of monomer, dimer and multiple subunit E3 ligases, and the in different cancer types, including GC (40). Whole‑genome HECTs will be described in the order of the NEDD4 family, sequencing revealed that RNF43 is mutated in 4.8% of HERC family and other HECT ligases. microsatellite‑stable and 54.6% of microsatellite‑unstable tumors (41). The mutational landscape of RNF43 may provide a 3. Structure and function of RING‑type E3 ligases in GC new approach to facilitate genome‑guided personalized therapy in GC. Overall, RNF43/ZNRF3 is a tumor suppressor and a Monomeric RING domain E3 ligase potential therapeutic target for GC. Therefore, five members of RING finger (RNF) domain subfamily. The RNF protein the RNF subfamily participate in regulating the development family contains a large number of members that are associ‑ of GC, where RNF6, RNF26, RNF38 and RNF185 function ated with several types of digestive system tumors, such as as carcinogenic factors, while RNF43/ZNRF3 acts as a tumor colorectal cancer and hepatocellular carcinoma (24,25). RNFs suppressor. also play a vital role in the occurrence of GC. RNF6 encodes a 685‑amino‑acid protein with a coiled‑coil domain at the Membrane‑associated RING‑CH (MARCH)8. MARCH8 is N‑terminus and a RING‑H2 finger at the C‑terminus (26). a member of the MARCH subfamily. A recent study identi‑ RNF38 shares a similar structure with RNF6 (27), and fied 11 E3 ligases that contained the RING‑CH domain and ONCOLOGY LETTERS 20: 22, 2020 3 (49) (80) (74) (15) (76) (85) (59) (43) (16) (33) Refs (112) (119) (139) (104) (130) (132) (101) (125) (140) (34,38) (67‑69) (92‑94) (99,100) (102,103) B κ

‑catenin/TCF Pathway

NA PI3K/AKT p53 NA Wnt/ AKT MDM2/ITGB1 NA SHP‑1/STAT3 AKT NA NA NA TRAF2/NF‑ p14ARF‑associated p53 p16/Rb IGF‑1R RhoA RhoA JWA/MARCH8/DR4 JWA/MARCH8/DR4 SHP‑1/STAT3 SHP‑1/STAT3 NA NA AKT AKT

Substrates

‑catenin; Lgr5 Cortactin; Snail1 DAB2IP P53 Snail1 PTEN P53; RUNX3 PARP‑1 SHP‑1 PTEN p27 FoxM1 p53 TRAF2 p14ARF β P53 GKN1 IGF‑1R; c‑Src, c‑Myc; RhoA; Brg1; GFI1 c‑Myc; RhoA; Brg1; DR4 SHP‑1 JWA NEK8 PHLPP1; FOX3 Expression Downregulated Upregulated Upregulated Downregulated Upregulated Upregulated Downregulated Upregulated Upregulated Upregulated Downregulated Upregulated Downregulated Downregulated Upregulated Upregulated Up/downregulated Downregulated Downregulated Downregulated Upregulated Upregulated Downregulated Upregulated

Subfamily RING/SCF HECT NEDD4 HECT RING/TRIM RING/SCF HECT NEDD4 HECT RING/MDM RING/NA RING/RNF NEDD4 HECT RING/SCF RING/SCF RING/CRL4 RING/NA RING/NA RING/PIRH HECT/Other RING/Cbl RING/SCF RING/RNF RING/MARCH RING/RNF RING/RNF RING/CRL2 RING/SCF

Family/ Gene ‑TRCP FBXL5 SMURF1 TRIM59 FBXO31 NEDD4‑1 MDM2 CHFR RNF6 WWP1 CHIP Cullin1 FBXL2 COP1 MKRN1 β PIRH2 UBR5 Cbl‑b FBXW7 RNF43 MARCH8 RNF38 RNF185 pVHL , 2019; , 2016 , 2013 , 2015 , 2017; et al et al et al et al et al , 2012 , 2018 , 2018; Kuai , 2009 , 2018 , 2015 , 2017 , 2012 , 2014 , 2014 , 2017 , 2016 , 2018 , 2008 , 2017; Zhou , 2013; Wang , 2017; Xu , 2014; Wu , 2018 et al , 2018 , 2017 , 2009 , 2015 , 2011 , 2016 , 2012 et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al et al Table Ⅰ. Characteristics of E3 ligase associated with gastric cancer. Table year Author, Che Zhang Kashima Wang Ko A Yang Zhang Huang Gao Qui Zhou Chi Liu Bai Li Cen Zou Huang Zhou Gao Li Ding Kim Tao Zhang Yang NA, not applicable. 4 WANG et al: E3 UBIQUITIN LIGASES IN GASTRIC CANCER

Figure 1. Regulation of important signaling pathways by E3 ubiquitin ligases in gastric cancer. The solid arrows represent activation, and flat‑headed arrows represent inhibition. RNF6 and RNF38 induce polyubiquitination of SHP‑1 and subsequently enhance STAT3 signaling in GC. GKN1 can be ubiquitinated by UBR5 E3 ligase and then activates the P16/Rb pathway. RNF185 can promote the ubiquitination of JWA and promote GC progression, and loss of JWA decrease the expression of MARCH8 in GC. MARCH8 promotes DR4 ubiquitination for degradation and then inhibites the progression of GC. CHIP facilitates TRAF2 ubiquitination for degradation and then inactivates NF‑κB signaling. RNF43 and SCF‑FBXW7 inhibit the progression of GC by inactivate Wnt/β‑catenin pathway and RhoA pathway. CHIP, C‑terminus of Hsp70‑interacting protein; DR4, ubiquitination of death receptor 4; FBXW7, F‑box/WD repeat‑containing protein 7; GKN1, gastrokine 1; JWA, PRA1 family protein 3; MARCH8, membrane‑associated RING‑CH8; Rb, retinoblastoma protein; RNF, RING finger domain; SCF, Skp1/cullin 1/F‑box protein complex; SHP‑1, tyrosine‑protein phosphatase non‑receptor type 6; TRAF2, TNF receptor‑associated factor 2; UBR5, ubiquitin protein ligase E3 component n‑recognin 5. The solid arrows means activate, and the flat tipped arrows means inhibit.

were named the MARCH1‑11 subfamily (42). The structure promote gastric carcinogenesis through this mechanism (53). of MARCH8 contains the RING‑CH domain and transmem‑ In summary, TRIM28, TRIM29 and TRIM59 play oncogenic brane domains. JWA is a downstream protein of RNF185 roles in gastric tumorigenesis, but only the regulatory mecha‑ ligase (33); it promotes the ubiquitination of death receptor 4 nism of TRIM59 has been elucidated. by increasing the expression of MARCH8 in GC cells, thereby reducing tumor necrosis factor‑related apoptosis‑inducing RING finger and CHY zinc‑finger domain containing 1 ligand‑mediated apoptosis (Fig. 1) (43). Moreover, MARCH8 (PIRH2). PIRH2 E3 ligases are crucial negative regulators of induces the apoptosis of GC cell lines by inactivating the PI3K p53 (Fig. 2). In addition to p53, many other proteins, such as p63, and β‑catenin/STAT3 signaling pathways (44). In summary, p73, c‑Myc, p27, DNA polymerase Eta and checkpoint kinase 2, MARCH8 is a tumor suppressor in GC. can be ubiquitylated by PIRH2 (55). PIRH2 plays an important role in the regulation of many types of tumors, such as glioma, Tripartite motif‑containing (TRIM) subfamily. TRIM proteins lung cancer and breast cancer (56‑58). In GC, PIRH2 is a key form a subfamily that regulates multiple cellular processes. E3 ligase of p53 ubiquitination, and silencing of PIRH2 causes TRIMs share a common N‑terminal tripartite domain, a RING p53 protein accumulation (59). This study also demonstrates domain, one or two B‑boxes and coiled‑coil domains (45). To that a microRNA (miR)‑100‑RNF144B‑PIRH2‑p53‑dependent date, three E3 ligases have been shown to be involved in the pathway might be a novel mechanism of ubiquitin‑mediated development and metastasis of GC. They are TRIM28 (also p53 degradation in GC cells (59). known as KAP1 or TIF1‑β), TRIM29 and TRIM59 (46‑49). TRIM28 is a universal transcriptional corepressor (50). The CBL subfamily. CBL proteins contain two highly conserved overexpression of TRIM28 causes peritoneal carcinoma‑ domains: The N‑terminal tyrosine kinase‑binding domain and tosis and poor prognosis in GC (47). Similar to TRIM28, the C3HC4 RING finger domain (60). The mammalian CBL the expression of TRIM29 is also upregulated in GC; the family consists of Cbl, Cbl‑b and c‑Cbl ligases (61). The three high expression of TRIM29 mRNA may be an independent members have similar functions, perhaps due to the specific predictor of lymph node metastasis and depth of invasion (48). structure. The c‑Cbl protein was the first CBL family protein TRIM59 has been reported in several human tumors and acts discovered, followed by Cbl‑b and Cbl (62). Previous studies on diverse signaling pathways, such as the focal adhesion have confirmed that all three CBL proteins are closely associ‑ kinase/AKT/matrix metalloproteinases pathway in epithelial ated with GC. In 2000, a study reported that the c‑Cbl protein ovarian cancer (51), the PI3K/AKT/mTOR pathway in human was frequently tyrosine phosphorylated in a tumor‑specific cholangiocarcinoma (52), the Wnt/β‑catenin signaling pathway manner in human GC tissues (63). Subsequently, c‑Cbl was in neuroblastoma (53), the NF‑κB pathway in non‑small cell found to be involved in stomach carcinogenesis by connecting lung cancer (54) and the p53 signaling pathway in GC (49). with the EGFR system (64). The p53 signaling pathway can be negatively regulated by Cbl‑b has a significant impact on the prognosis and drug the E3 ligase TRIM59, which enhances the ubiquitination sensitivity of GC, and a previous study showed that Cbl‑b is an and subsequent degradation of p53 (Fig. 2). TRIM59 might oncogene (64). However, subsequent studies provide different ONCOLOGY LETTERS 20: 22, 2020 5

ubiquitination of tumor suppressor ARF (p14ARF) was described in 2011 (76). MKRN1 induces the ubiquitination and degradation of p14ARF and downregulated p14ARF expression (Fig. 2) (76). Furthermore, MKRN1 overexpression was associated with well‑differentiated gastric carcinoma, whereas p14ARF overexpression was associated with poorly differentiated gastric carcinoma. FIGC, a novel FGF‑induced ubiquitin‑protein ligase, consists of an N‑terminal RING finger module and proline‑rich region at the C‑terminus. Only one study has shown that FIGC probably functions as an E3 ligase and is implicated in carcinogenesis through the dysregulation of fibroblast growth modulator (77). In brief, further research is needed to confirm the mechanism of these two E3 ligases in GC.

Dimeric RING domain E3 ligases Figure 2. Regulation of the p53 signaling pathway by binding and ubiqui‑ MDM2. Dimeric RING domain E3 ligases can be classified tylation of tumor‑regulating proteins in GC. The solid arrows represent into homodimers and heterodimers. MDM2, a heterodimeric activation, and flat‑headed arrows represent inhibition. MKRN1 induces the ubiquitination and degradation of p14ARF and then downregulates RING ligase, was originally identified as a ubiquitin ligase the expression of MDM2. MDM2, PIRH2, TRIM59 and COP1 directly E3 that promotes the degradation of tumor suppressor p53 bind to p53, and they promote p53 degradation in the UPS to promote GC (Fig. 2) (78). Subsequent studies suggest that MDM2 can progression. Cullin1 facilitates P27 ubiquitination for degradation and then ubiquitinate and degrade multiple signaling molecules in GC, regulates cell cycle of GC. GC, gastric cancer; CRL4, cullin‑RING ligase 4; COP1, constitutive photomorphogenic 1; MDM2, MDM2 proto‑oncogene; including p53, forkhead box protein O3A (FOXO3A) and MKRN1, makorin RING finger protein 1; p14ARF, tumor suppressor ARF; runt‑related transcription factor 3 (RUNX3) (78‑81). Human PIRH2, RING finger and CHY zinc‑finger domain‑containing 1; SPA1, hTERT can interact with MDM2 and dramatically increase suppressor of PHYA‑1; TRIM59, tripartite motif; Ub, ubiquitin; UPS, the ubiquitination of FOXO3A, resulting in the invasion of ubiquitin‑proteasome system. The solid arrows means activate, and the flat tipped arrows means inhibit. GC cells (79). RUNX3 is known as a tumor suppressor (82). MDM2 ligases can recognize Lys94 and Lys148 of RUNX3 and decrease the expression levels of RUNX3 (80). Overall, MDM2 acts as a carcinogenic factor in GC by affecting perspectives, in which Cbl‑b is found to enhance the sensi‑ different signaling proteins. tivity to 5‑fluorouracil and cetuximab in GC cells through the ubiquitination pathway (65,66). Other studies have also C‑terminus of Hsp70‑interacting protein (CHIP). CHIP indicated that Cbl‑b inhibits tumor metastasis and growth in includes a C‑terminal U‑box domain and an N‑terminal multiple drug‑resistant (MDR) gastric and breast cancer cells, tetratricopeptide repeat domain, which have E3 ubiquitin as well as increasing the sensitivity of MDR cells to anticancer ligase activity and interact with the molecular chaperones drugs (67‑69). These findings provide a new research direction Hsc70‑Hsp70 and Hsp90, respectively (83). CHIP is character‑ for the chemotherapy and targeted therapy of GC. ized as a homologous dimeric RING ligase and antioncogene Cbl, in conjunction with the EGFR system, might be related in human cancer (15,84). The U‑box domain of CHIP facili‑ to gastric carcinogenesis and metastasis (70). In summary, tates TNF receptor‑associated factor 2 ubiquitination for Cbl and c‑Cbl are oncogenes in GC, whereas Cbl‑b can act degradation and then inactivates NF‑κB signaling (Fig. 1). as an oncogene or tumor suppressor, and only its regulatory A previous study also showed that CHIP expression prevents mechanism has been well clarified among the three members. the angiogenesis and metastasis of GC (85). Above all, CHIP overexpression is correlated with good prognosis in GC Checkpoint with forkhead and RING finger domains protein patients, and targeting CHIP may be a new approach in GC (CHFR). Previous studies have reported that the aber‑ therapy. rant methylation of CHFR promotes the development of GC (71,72). As an E3 ligase, CHFR contains an N‑terminal Multi‑subunit RING domain E3 ligases forkhead‑associated domain, a central RING domain and SCF subfamily. The CRL1 complex comprises SKP1, a C‑terminal cysteine‑rich region (73). PARP‑1 may be a CUL1, RING box1 (RBX1) and a member of the F‑box substrate by CHFR for ubiquitination and degradation in GC; protein family (86). The F‑box protein family can be further this process leads to cell cycle arrest before entering mitosis categorized into three subclasses: i) FBXW; ii) F‑box and and inhibits the proliferation of GC cells (74). Thus, CHFR leucine‑rich repeat (FBXL); and iii) F‑boxes containing other functions as a tumor suppressor in GC. domain motifs (FBXO) proteins. Each subunit of SCF has unique features as follows: i) CUL1 serves as a rigid molecular Makorin‑1 (MKRN1) and FGF‑induced in gastric cancer scaffold protein; ii) RBX1 contains a RING finger domain (FIGC). These two E3 ligases are rarely mentioned in GC. for the recruitment of E2 enzyme; iii) SKP1 functions as an MKRN1 was first identified owing to its interaction with human adaptor; iv) F‑box proteins act as a substrate‑determining telomerase reverse transcriptase (TERT) and modulation of component (86,87), many of them function as E3 ligase and telomere length homeostasis (75). The MKRN1‑mediated will be discussed in detail below. 6 WANG et al: E3 UBIQUITIN LIGASES IN GASTRIC CANCER

FBXW proteins. The WD repeat domain comprises a 44‑60 residue sequence that typically contains the GH dipeptide 11‑24 residues from its N‑terminus and the WD dipeptide at the C‑terminus (88). This class of E3 ligases mainly recognizes proteins involved in cell cycle regulation and tumorigenesis, thereby regulating cancerous growth. FBXW7 and β‑transducin repeat‑containing protein (β‑TRCP) are directly correlated with the progression of GC in the form of E3 ligases (89,90). FBXW7 is a well‑characterized SCF in GC and facilitates the destruction of oncogenic proteins, such as c‑Myc, trans‑ forming protein RhoA (RhoA), transcription activator BRG1 (Brg1) and zinc‑finger protein GFI‑1 (GFI1) (90‑93). These targeted proteins all govern gastric tumorigenesis; for example, Brg1 promotes the metastasis of GC (92), RhoA has been impli‑ cated in gastric tumorigenesis (Fig. 1) (94), and GFI1 promotes GC cell proliferation as an oncoprotein (93). FBXW7 is also regulated by several upstream signaling molecules. Previous studies indicated that microRNAs and long noncoding RNAs Figure 3. Regulation of the PI3K/AKT pathway by binding and ubiquitylation are involved in the occurrence and development of GC by of tumor‑regulating proteins in gastric cancer. The solid arrows represent altering the expression of FBXW7 (95,96). Therefore, FBXW7 activation. β‑TRCP promotes PHLPP1 ubiquitination for degradation and is a complex tumor suppressor in GC because of its involve‑ then regulates the phosphorylation of AKT. NEDD4 and WWP1 have the similar functions by promoting the ubiquitination of PTEN. SMURF1 ment in numerous upstream and downstream signals. regulates the phosphorylation of PI3K and AKT by ubiquitinating DAB2IP. β‑TRCP has two distinct isoforms, β‑TRCP1 and β‑TRCP2, β‑T RCP, β‑transducin repeat‑containing protein; DAB2IP, DAB2 interacting which share similar biochemical properties (97). It was reported protein; NEDD4, neural precursor cell expressed developmentally downreg‑ that β‑TRCP1 and β‑TRCP2 were predominantly expressed in ulated protein 4; PHLPP1, PH domain leucine‑rich repeat‑containing protein phosphatase 1; SCF, Skp1/cullin 1/F‑box protein complex; SMURF1, Smad the stomach and the small intestine, respectively. A previous ubiquitin regulatory factor 1; WWP1, WW domain containing E3 ubiquitin study showed that β‑TRCP2 might promote gastric carcinogen‑ protein ligase 1; Ub, ubiquitin. esis through the activation of the Wnt signaling pathway (98). Moreover, β‑TRCPs participate in the regulation of the AKT signaling pathway (Fig. 3) and epidermal growth factor receptor/glycogen synthase kinase‑3β/FOXP3 axis through the the G1 phase of the cell cycle (111). Before these findings, ubiquitination of PH domain leucine‑rich repeat‑containing immunohistochemistry results suggested that high expression protein phosphatase 1 and FOX3, respectively (99,100). One levels of CUL1 were detected in 60% of all GC tissues, in a previous study has reported that β‑TRCP can serve as a tumor study of 792 patients (112). Further in vitro studies showed that suppressor or oncoprotein in the etiology of a variety of cancers increased CUL1 expression was correlated with poor patient depending on the type of tumor tissue (99). Nevertheless, survival by decreasing p27 expression (112) (Fig. 2). Therefore, β‑TRCP might serve as an oncoprotein in GC. CUL1, an oncoprotein, can be regarded as a prognostic biomarker of GC. FBXL and FBXO proteins. FBXL proteins contain leucine‑rich repeat sequences. FBXL2 and FBXL5 exhibit Von Hippel‑Lindau disease tumor suppressor (pVHL). Von similar characteristics in GC (101,102). FBXL2 promotes the Hippel‑Lindau disease was first considered to be a heritable ubiquitination and degradation of FOXM1, which then inhibits cancer syndrome characterized by retinal and neuronal GC proliferation (101). Similarly, FBXL5 can also suppress hemangioblastoma owing to a mutation in the VHL gene (113). GC cell migration by the ubiquitination‑mediated destruction Although the pVHL protein itself displays no enzymatic of Cortactin and Snail1 (102,103). FBXO31, a member of the activity, pVHL functions as a substrate recognition subunit third class of the F‑box protein family, can also target Snail1 in CRL2 E3 ligases after binding with the elongin and CUL for its ubiquitylation and degradation (104). Hence, FBXL2, proteins (114). pVHL is a tumor suppressor in renal cell carci‑ FBXL5 and FBXO31 exert tumor inhibitory roles in GC. noma (RCC) (115,116). Serine/threonine‑protein kinase NEK8 is a serine/threonine‑specific protein kinase family member CUL1. CUL1 is a member of the CUL family and acts as a that serves a role in the progression of mitosis and carcinogen‑ scaffold protein of the SCF ubiquitin E3 ligase (105). CUL1 is esis (117). NEK8 is reported to be a novel target of pVHL in the modified by the ubiquitin‑like protein NEDD8 and enhances regulation of RCC and GC (118,119); pVHL promotes NEK8 the activity of SCF ligases to p27 (106). Several studies have protein degradation via the proteasome‑ubiquitin pathway in shown that diverse types of human malignant tumors are GC cells (119). In summary, the E3 ligase pVHL targets NEK8 related to CUL1. CUL1 can facilitate cell proliferation in and inhibits the proliferation, colony formation and migration osteosarcoma, breast cancer, prostate cancer and lung cancer of GC (119). in vitro and in vivo (107‑110). In addition, the co‑expression of CUL1 and CUL2 induces the initiation of carcinogenesis COP1. COP1 protein structure comprises an N‑terminal in colorectal cancer by arresting p53‑positive colon cells in RING finger region, a coiled‑coil domain and seven WD40 ONCOLOGY LETTERS 20: 22, 2020 7 repeats at its C‑terminus (120). COP1 is well studied in plants, These findings suggested that WWP1 might be a valuable but it has been little studied in humans. COP1 is known as prognostic marker and potential target in the treatment of GC. a central repressor in the light signaling pathway and forms a complex with suppressor of PHYA‑1 (COP1‑SPA1) (121). Smurf1. Smurf1 was first recognized in selective interac‑ This complex interacts with the CUL4‑DDB1 ligase, which tions with receptor‑regulated SMADs, which led to its belongs to the CRL4 family, to form CUL4‑DDB1COP1‑SPA1 initial naming (135). Smurf1 contains two WW domains and ligases in plants (122). However, the catalytic mechanism negatively regulates the transforming growth factor‑β/bone of COP1 has not been fully elucidated in humans. Previous morphogenetic protein signaling (136). DAB2‑interacting studies revealed that the ubiquitin ligase COP1 promoted the protein (DAB2IP), a tumor suppressor, is known to be progression of multiple cancer types in vitro, including GC, by downregulated in GC (137); Smurf1 significantly promotes downregulating the expression of p53 (Fig. 2) (123‑125). The the ubiquitination‑dependent degradation of DAB2IP role of COP1 in GC is controversial (123‑126). One previous (Fig. 3) (138). In addition, a subsequent study concluded that study indicates that low COP1 expression resulted in poorer the Smurf1/DAB2IP signaling axis has an important impact prognoses in patients with GCs (126); however, more studies in GC (139). Overall, Smurf1 might act an oncoprotein in GC. have suggested that COP1 functions as an oncogene (123‑125). In summary, there are eight multi‑subunit RING domain Other HECT ligases E3 ligases associated with GC, including six SCFs, one CRL2 UBR5. UBR5 is the only member of Other HECT ligase family ligase and one CRL4 ligase. Among these eight CRLs, β‑T RCP, that serves a role in regulating GC cell growth (140). Structurally, CUL1 and COP1 are oncoproteins, whereas FBXW7, FBXL2, UBR5 is composed of an N‑terminal ubiquitin‑associated FBXL5, FBXO31 and pVHL act as tumor suppressors. domain, two nuclear localization signals, a ubiquitin recognin box domain, a C‑terminal poly(A)‑binding domain and a 4. Structure and function of HECT‑type E3 ligases in GC HECT domain at its far C‑terminus (141). A previous study showed that UBR5 gene mutations occur in 27.8% of GC NEDD4 subfamily. The E3 ligases of the NEDD4 subfamily and 23.3% of colorectal cancer (142). Gastrokine 1, a gastric are characterized by an N‑terminal C2 domain responsible tumor suppressor, can be downregulated by UBR5 E3 ligase for subcellular localization, between two and four WW (Fig. 1), and the overexpression of UBR5 is associated with domains that recruit substrates and a HECT domain at the poor overall and disease‑free survival (140). Thus, UBR5 may C‑terminus (127). Three NEDD4 subfamily members might serve as a carcinogenic agent and a prognostic factor in GC. be related to GC, including NEDD4‑1, WWP1 and Smurf1, and they will be elaborated below. 5. Therapeutics targeting E3 ligases in GC

NEDD4‑1. NEDD4‑1 contains four WW domains and is an E3 ligases have potent effects on the origin, progression and ancestral member of the NEDD4 family (23). Previous studies prognosis of GC through a series of signaling pathways. E3 have indicated that NEDD4‑1 is frequently overexpressed ligase‑targeting molecules and drugs may provide a new in several types of human cancers, including hepatocellular approach to GC treatment. Bortezomib was the first proteasome carcinoma, lung cancer and gastrointestinal cancer (128‑130). inhibitor approved by the US Food and Drug Administration A range of tumor suppressors can be ubiquitinated by in multiple myeloma (143). In vitro, bortezomib has a signifi‑ NEDD4‑1, including PTEN, c‑Myc and large tumor suppressor cant negative effect on the growth of GC cells (144). It is kinase 1 (128,131). Immunohistochemical analysis conducted possible that bortezomib may become a common adjuvant by Kim et al (130) showed that NEDD4‑1 is overexpressed therapeutic target in GC because it has a significant negative in colorectal and gastric carcinomas. NEDD4‑1 was also effect on the proliferation of GC cells (144). However, only a found to promote GC cell migration and invasion (129). As a few E3 ligase‑targeting molecules have the ability to suppress carcinogenic factor, the targets of NEDD4‑1 remain unclear the progression of GC. in human GC, and further studies are needed to explore this APG115 has been identified as a novel inhibitor of MDM2 research topic. ligase, and its potential for treating GC has been shown in vitro and in vivo (145). In vitro, APG115 inhibited the proliferation WW domain‑containing 1 (WWP1). WWP1 is another of GC cell lines that harbored MDM2 expression by down‑ GC‑related member of the NEDD4 subfamily that also has regulating the mRNA expression of MDM2. In a xenograft four WW domains. Similar to NEDD4‑1, WWP1 has been mouse model, APG115 contributed to a smaller GC tumor revealed as a versatile E3 ligase with a large repertoire of size and enhanced the effect of radiotherapy. As previously substrates (23). In GC cell lines, WWP1 is overexpressed, mentioned, MDM2 downregulates several tumor suppressors and is closely associated with worse survival by regulating in GC. Consequently, the MDM2 inhibitor APG115 may be the PTEN‑AKT signaling pathway in patients with GC applied for GC treatment in the future. (Fig. 3) (132). The overall survival rate of patients who were Nutlin proteins were identified in 2004 as the first selec‑ positive for WWP1 protein was 25.9%, whereas it was 66.0% tive small molecules of MDM2, which could antagonize in patients who without WWP1 protein in China in 2015 (132). p53‑MDM2 binding (146). Among the nutlins, only nutlin‑3 Subsequent studies further confirmed that WWP1 might play represents a promising therapeutic candidate for drug devel‑ a role as an oncogene in GC. miR‑584‑5p, miR‑129‑5p and opment in human cancer (147). Over the past decade, it has miR‑129‑3p were found to suppress WWP1 protein expression been confirmed that nutlin‑3 can induce cell growth arrest and inhibit the proliferation of GC in vivo and in vitro (133,134). and apoptosis in a number of cancer cell types (148,149). In 8 WANG et al: E3 UBIQUITIN LIGASES IN GASTRIC CANCER p53‑defective cancer cells, there is a synergistic effect between degradation in human cancers (158). Compounds and small nutlin‑3 and bortezomib; cotreatment with bortezomib and molecules targeting E3 ligases may become underlying nutlin‑3 significantly induce paraptosis and cell death (150). templates for the synthesis of targeted therapeutic drugs in Nutlin‑3 has not been used in the treatment of GC; however, GC. However, there are still many obstacles to overcome the antitumor activity of nutlin‑3 against GC cells has been before the application of compounds targeting E3 ligases demonstrated in vivo and in vitro (151). It has been reported in GC, such as the detection and analysis of their complex that nutlin‑3 induces G1 arrest in MKN‑45 and SNU‑1 gastric functional mechanisms and molecular structures. Therefore, adenocarcinoma cell lines in vitro, and the activation of p53 further studies should aim to reveal the molecular mechanism by nutlin‑3 effectively increased the incidence of apoptosis of individual E3 ligases in different subtypes of GC, and deter‑ in wild‑type p53 GC cells. In vivo, the combined treatment mine the structure of these targeting compounds to facilitate of nutlin‑3 and fluorouracil led to a more potent inhibitory further synthesis of such targeted therapy drugs. In conclusion, effect on the tumor growth of experimental animals compared E3 ligases are crucial tumor regulatory factors and potential with treatment with each agent alone. Overall, nutlin‑3 is a therapeutic targets in GC. broad‑spectrum antitumor agent and has the potential to be used in the treatment of GC by targeting the E3 ligase MDM2. Acknowledgements Triptolide is a compound purified from tripterygium wilfordii that exhibits antitumor effects in GC (152‑155). In Not applicable. 1991, Chinese scholars found that triptolide had antitumor activity in a variety of cancer cell lines, including GC (152). Funding A subsequent study demonstrated that triptolide treatment of GC cells containing wild‑type p53 gene resulted in a signifi‑ This research was funded by The National Natural Science cant inhibitory effect on cell growth, whereas GC cells with Foundation of China (grant no. 30871207), The National mutant p53 did not exhibit this effect (153). Another study Natural Science Foundation of China (grant nos. 81874063 indicated that this p53‑dependent antitumor activity was and 81672389) and Anhui Province Science and Technology achieved by inhibiting the overexpression of MDM2 (154). Key Project (grant no. 1704a0802176). Moutan cortex is another Traditional Chinese Medicine that can also induce apoptosis through the MDM2‑p53‑dependent Availability of data and materials pathway in GC cells (155). Therefore, Chinese herbs, such as triptolide and moutan cortex, might be potential anticancer Not applicable. agents for GC. MLN4924, a neddylation inhibitor, is an indirect inhibitor Authors' contributions of CRL E3 ligases. MLN4924 acts as a promoter of apop‑ tosis and is a potential anticancer drug in diverse types of MW and YL developed the concept of the manuscript. MW, human cancers, including GC (156). It has been reported that WD and ZK were responsible for writing, reviewing and editing MLN4924 downregulates the expression of CRLs and then the manuscript. WD participated in revising the manuscript. ZK suppresses the growth of GC cells. There are some other supervised the project. YL was involved with the project admin‑ small molecules that can also target E3 ligase. miR‑223 can istration. All authors read and approved the final manuscript. target FBXW7 and downregulate its expression, so drugs that promote degradation of miR‑223 may be useful in patients Ethics approval and consent to participate with GC (157). As aforementioned, WWP1 is an oncoprotein in GC, and miR‑584‑5p, miR‑129‑5p and miR‑129‑3p suppress Not applicable. WWP1 protein expression and inhibit the proliferation of GC (133,134). Thus, miRNAs may also be a research direction Patient consent for publication for E3‑targeted therapy for GC. In summary, there are still no drugs targeting E3 used in the clinical treatment of GC, and Not applicable. the effects of the compounds mentioned above are still in the research stage. Competing interests

6. Conclusions and perspectives The authors declare that they have no competing interests.

Over the past few years, an increasing number of E3 ligases have been described as tumor regulators in GC. The present References review summarizes approximately thirty types of E3 ligases 1. Torre LA, Bray F, Siegel RL, Ferlay J, Lortet‑Tieulent J and that play essential roles in regulating the development of GC, Jemal A: Global cancer statistics, 2012. CA Cancer J Clin 65: including RING and HECT ligases. The function and signifi‑ 87‑108, 2015. cance of E3 ligases in GC has been well examined, but several 2. Wu Y, Fan Y, Jiang Y, Wang Y, Liu H and Wei M: Analysis of risk factors associated with precancerous lesion of gastric cancer E3 ligases, such as COP1, need further studies to elucidate in patients from eastern China: A comparative study. J Cancer their mechanisms. It has been shown that many synthetic and Res Ther 9: 205‑209, 2013. 3. Zeng H, Zheng R, Guo Y, Zhang S, Zou X, Wang N, Zhang L, natural compounds targeting E3 ligases could regulate the Tang J, Chen J, Wei K, et al: Cancer survival in China, 2003‑2005: level of various signaling proteins through UPS‑mediated A population‑based study. Int J Cancer 136: 1921‑1930, 2015. ONCOLOGY LETTERS 20: 22, 2020 9

4. Woo Y, Goldner B, Son T, Song K, Noh SH, Fong Y and 27. Eisenberg I, Hochner H, Levi T, Yelin R, Kahan T and Hyung WJ: Western validation of a novel gastric cancer prog‑ Mitrani‑Rosenbaum S: Cloning and characterization of a novel nosis prediction model in US gastric cancer patients. J Am Coll human gene RNF38 encoding a conserved putative protein with Surg 226: 252‑258, 2018. a RING finger domain. Biochem Biophys Res Commun 294: 5. Wen T, Wang Z, Li Y, Li Z, Che X, Fan Y, Wang S, Qu J, Yang X, 1169‑1176, 2002. Hou K, et al: A four‑factor immunoscore system that predicts 28. Katoh M: Molecular cloning and characterization of RNF26 on clinical outcome for stage II/III gastric cancer. Cancer Immunol human chromosome 11q23 region, encoding a novel RING finger Res 5: 524‑534, 2017. protein with leucine zipper. Biochem Biophys Res Commun 282: 6. Abramov IS, Emelyanova MA, Ryabaya OO, Krasnov GS, 1038‑1044, 2001. Zasedatelev AS and Nasedkina TV: Somatic mutations associ‑ 29. Jongsma ML, Berlin I, Wijdeven RH, Janssen L, Janssen GM, ated with metastasis in acral melanoma. Mol Biol (Mosk) 53: Garstka MA, Janssen H, Mensink M, van Veelen PA, 648‑653, 2019 (In Russian). Spaapen RM and Neefjes J: An ER‑associated pathway defines 7. Hou YC and Deng JY: Role of E3 ubiquitin ligases in gastric endosomal architecture for controlled cargo transport. Cell 166: cancer. World J Gastroenterol 21: 786‑793, 2015. 152‑166, 2016. 8. Hickey CM, Xie Y and Hochstrasser M: DNA binding by the 30. Qin Y, Zhou MT, Hu MM, Hu YH, Zhang J, Guo L, Zhong B MATα2 transcription factor controls its access to alternative and Shu HB: RNF26 temporally regulates virus‑triggered ubiquitin‑modification pathways. Mol Biol Cell 29: 542‑556, 2018. type I interferon induction by two distinct mechanisms. PLoS 9. Bulatov E, Valiullina A, Sayarova R and Rizvanov A: Promising Pathog 10: e1004358, 2014. new therapeutic targets for regulation of inflammation and 31. Wang R, Zhao X, Xu J, Wen Y, Li A, Lu M and Zhou J: Astrocytic immunity: RING‑type E3 ubiquitin ligases. Immunol Lett 202: JWA deletion exacerbates dopaminergic neurodegeneration by 44‑51, 2018. decreasing glutamate transporters in mice. Cell Death Dis 9: 352, 10. Lu W, Yang C, He H and Liu H: The CARM1‑p300‑c‑Myc‑Max 2018. (CPCM) transcriptional complex regulates the expression of 32. Zhu T, Chen R, Li A, Liu J, Gu D, Liu Q, C Chang H and Zhou J: CUL4A/4B and affects the stability of CRL4 E3 ligases in JWA as a novel molecule involved in oxidative stress‑associated colorectal cancer. Int J Biol Sci 16: 1071‑1085, 2020. signal pathway in myelogenous leukemia cells. J Toxicol Environ 11. Liu L, Wong CC, Gong B and Yu J: Functional significance and Health A 69: 1399‑1411, 2006. therapeutic implication of ring‑type E3 ligases in colorectal 33. Qiu D, Wang Q, Wang Z, Chen J, Yan D, Zhou Y, Li A, Zhang R, cancer. Oncogene 37: 148‑159, 2018. Wang S and Zhou J: RNF185 modulates JWA ubiquitination and 12. Uchida C and Kitagawa M: RING‑, HECT‑, and RBR‑type E3 promotes gastric cancer metastasis. Biochim Biophys Acta Mol ubiquitin ligases: Involvement in human cancer. Curr Cancer Basis Dis 1864: 1552‑1561, 2018. Drug Targets 16: 157‑174, 2016. 34. Gao Y, Cai A, Xi H, Li J, Xu W, Zhang Y, Zhang K, Cui J, Wu X, 13. Johansson H, Isabella Tsai YC, Fantom K, Chung CW, Kümper S, Wei B and Chen L: Ring finger protein 43 associates with gastric Martino L, Thomas DA, Eberl HC, Muelbaier M, House D and cancer progression and attenuates the stemness of gastric cancer Rittinger K: Fragment‑based covalent ligand screening enables stem‑like cells via the Wnt‑β/catenin signaling pathway. Stem rapid discovery of inhibitors for the RBR E3 ubiquitin ligase Cell Res Ther 8: 98, 2017. HOIP. J Am Chem Soc 141: 2703‑2712, 2019. 35. Xi HQ, Cai AZ, Wu XS, Cui JX, Shen WS, Bian SB, Wang N, 14. Yu JM, Sun W, Wang ZH, Liang X, Hua F, Li K, Lv XX, Li JY, Lu CR, Song Z, et al: Leucine‑rich repeat‑containing Zhang XW, Liu YY, Yu JJ, et al: TRIB3 supports breast cancer G‑protein‑coupled receptor 5 is associated with invasion, metas‑ stemness by suppressing FOXO1 degradation and enhancing tasis, and could be a potential therapeutic target in human gastric SOX2 transcription. Nat Commun 10: 5720, 2019. cancer. Br J Cancer 110: 2011‑2020, 2014. 15. Zhang J, Wu H, Yi B, Zhou J, Wei L, Chen Y and Zhang L: RING 36. Li XB, Yang G, Zhu L, Tang YL, Zhang C, Ju Z, Yang X and finger protein 38 induces gastric cancer cell growth by decreasing Teng Y: Gastric Lgr5(+) stem cells are the cellular origin of inva‑ the stability of the protein tyrosine phosphatase SHP‑1. FEBS sive intestinal‑type gastric cancer in mice. Cell Res 26: 838‑849, Lett 592: 3092‑3100, 2018. 2016. 16. Huang Z, Cai Y, Yang C, Chen Z, Sun H, Xu Y, Chen W, Xu D, 37. Barker N, Huch M, Kujala P, van de Wetering M, Snippert HJ, Tian W and Wang H: Knockdown of RNF6 inhibits gastric van Es JH, Sato T, Stange DE, Begthel H, van den Born M, et al: cancer cell growth by suppressing STAT3 signaling. Onco Lgr5(+ve) stem cells drive self‑renewal in the stomach and Targets Ther 11: 6579‑6587, 2018. build long‑lived gastric units in vitro. Cell Stem Cell 6: 25‑36, 17. Berndsen CE and Wolberger C: New insights into ubiquitin E3 2010. ligase mechanism. Nat Struct Mol Biol 21: 301‑307, 2014. 38. Zhou Y, Lan J, Wang W, Shi Q, Lan Y, Cheng Z and Guan H: 18. Ohi MD, Vander Kooi CW, Rosenberg JA, Chazin WJ and ZNRF3 acts as a tumour suppressor by the Wnt signalling Gould KL: Structural insights into the U‑box, a domain associ‑ pathway in human gastric adenocarcinoma. J Mol Histol 44: ated with multi‑ubiquitination. Nat Struct Biol 10: 250‑255, 2003. 555‑563, 2013. 19. Leslie PL, Ke H and Zhang Y: The MDM2 RING domain and 39. Nanki K, Toshimitsu K, Takano A, Fujii M, Shimokawa M, central acidic domain play distinct roles in MDM2 protein Ohta Y, Matano M, Seino T, Nishikori S, Ishikawa K, et al: homodimerization and MDM2‑MDMX protein heterodimeriza‑ Divergent routes toward Wnt and R‑spondin niche independency tion. J Biol Chem 290: 12941‑12950, 2015. during human gastric carcinogenesis. Cell 174: 856‑869.e17, 2018. 20. Genschik P, Sumara I and Lechner E: The emerging family of 40. Hao HX, Jiang X and Cong F: Control of Wnt receptor turnover CULLIN3‑RING ubiquitin ligases (CRL3s): Cellular functions by R‑spondin‑ZNRF3/RNF43 signaling module and its dysregu‑ and disease implications. EMBO J 32: 2307‑2320, 2013. lation in cancer. Cancers (Basel) 8: pii: E54, 2016. 21. Kelsall IR, Kristariyanto YA, Knebel A, Wood NT, Kulathu Y 41. Wang K, Yuen ST, Xu J, Lee SP, Yan HH, Shi ST, Siu HC, and Alpi AF: Coupled monoubiquitylation of the co‑E3 ligase Deng S, Chu KM, Law S, et al: Whole‑genome sequencing and DCNL1 by Ariadne‑RBR E3 ubiquitin ligases promotes comprehensive molecular profiling identify new driver mutations cullin‑RING ligase complex remodeling. J Biol Chem 294: in gastric cancer. Nat Genet 46: 573‑582, 2014. 2651‑2664, 2019. 42. Liu H, Mintern JD and Villadangos JA: MARCH ligases in 22. Weber J, Polo S and Maspero E: HECT E3 ligases: A tale with immunity. Curr Opin Immunol 58: 38‑43, 2019. multiple facets. Front Physiol 10: 370‑377, 2019. 43. Wang Q, Chen Q, Zhu L, Chen M, Xu W, Panday S, Wang Z, Li A, 23. Lorenz S: Structural mechanisms of HECT‑type ubiquitin Røe OD, Chen R, et al: JWA regulates TRAIL‑induced apoptosis ligases. Biol Chem 399: 127‑145, 2018. via MARCH8‑mediated DR4 ubiquitination in cisplatin‑resistant 24. Geng R, Tan X, Wu J, Pan Z, Yi M, Shi W, Liu R, Yao C, Wang G, gastric cancer cells. Oncogenesis 6: e353, 2017. Lin J, et al: RNF183 promotes proliferation and metastasis of 44. Yin J, Ji Z, Hong Y, Song Z, Hu N, Zhuang M, Bian B, Liu Y and colorectal cancer cells via activation of NF‑κB‑IL‑8 axis. Cell Wu F: Sh‑MARCH8 inhibits tumorigenesis via PI3K pathway in Death Dis 8: e2994, 2017. gastric cancer. Cell Physiol Biochem 49: 306‑321, 2018. 25. Peng R, Zhang PF, Yang X, Wei CY, Huang XY, Cai JB, Lu JC, 45. Sun M, Li S, Yu K, Xiang J and Li F: An E3 ubiquitin ligase Gao C, Sun HX, Gao Q, et al: Overexpression of RNF38 facili‑ TRIM9 is involved in WSSV infection via interaction with tates TGF‑β signaling by Ubiquitinating and degrading AHNAK β‑TrCP. Dev Comp Immunol 97: 57‑63, 2019. in hepatocellular carcinoma. J Exp Clin Cancer Res 38: 113, 2019. 46. Sun Y, Keown JR, Black MM, Raclot C, Demarais N, Trono D, 26. Macdonald DH, Lahiri D, Sampath A, Chase A, Sohal J and Turelli P and Goldstone DC: A dissection of oligomerization by Cross NC: Cloning and characterization of RNF6, a novel RING the TRIM28 tripartite motif and the interaction with members of finger gene mapping to 13q12. Genomics 58: 94‑97, 1999. the Krab‑ZFP family. J Mol Biol 431: 2511‑2527, 2019. 10 WANG et al: E3 UBIQUITIN LIGASES IN GASTRIC CANCER

47. Yokoe T, Toiyama Y, Okugawa Y, Tanaka K, Ohi M, Inoue Y, 68. Xu L, Zhang Y, Qu X, Che X, Guo T, Cai Y, Li A, Li D, Li C, Mohri Y, Miki C and Kusunoki M: KAP1 is associated with Wen T, et al: E3 ubiquitin ligase Cbl‑b prevents tumor metastasis peritoneal carcinomatosis in gastric cancer. Ann Surg Oncol 17: by maintaining the epithelial phenotype in multiple drug‑resis‑ 821‑828, 2010. tant gastric and breast cancer cells. Neoplasia 19: 374‑382, 48. Kosaka Y, Inoue H, Ohmachi T, Yokoe T, Matsumoto T, 2017. Mimori K, Tanaka F, Watanabe M and Mori M: Tripartite 69. Zhang Y, Qu X, Hu X, Yang X, Hou K, Teng Y, Zhang J, Sada K motif‑containing 29 (TRIM29) is a novel marker for lymph node and Liu Y: Reversal of P‑glycoprotein‑mediated multi‑drug metastasis in gastric cancer. Ann Surg Oncol 14: 2543‑2549, resistance by the E3 ubiquitin ligase Cbl‑b in human gastric 2007. adenocarcinoma cells. J Pathol 218: 248‑255, 2009. 49. Zhou Z, Ji Z, Wang Y, Li J, Cao H, Zhu HH and Gao WQ: TRIM59 70. Lai AZ, Durrant M, Zuo D, Ratcliffe CD and Park M: Met is up‑regulated in gastric tumors, promoting ubiquitination and kinase‑dependent loss of the E3 ligase Cbl in gastric cancer. degradation of p53. Gastroenterology 147: 1043‑1054, 2014. J Biol Chem 287: 8048‑8059, 2012. 50. Ma X, Zhang S, Zhang M, Zhu Y, Ma P, Yang S, Su L, Li Z, Lv W 71. Gao YJ, Xin Y, Zhang JJ and Zhou J: Mechanism and patho‑ and Luan W: TRIM28 down‑regulation on methylation imprints biologic implications of CHFR promoter methylation in gastric in bovine preimplantation embryos. Zygote 26: 449‑456, carcinoma. World J Gastroenterol 14: 5000‑5007, 2008. 2018. 72. Li Y, Yang Y, Lu Y, Herman JG, Brock MV, Zhao P and Guo M: 51. Zhang P, Zhang H, Wang Y, Zhang P and Qi Y: Tripartite Predictive value of CHFR and MLH1 methylation in human motif‑containing protein 59 (TRIM59) promotes epithe‑ gastric cancer. Gastric Cancer 18: 280‑287, 2015. lial ovarian cancer progression via the focal adhesion 73. Satoh A, Toyota M, Itoh F, Sasaki Y, Suzuki H, Ogi K, Kikuchi T, kinase(FAK)/AKT/matrix metalloproteinase (MMP) pathway. Mita H, Yamashita T, Kojima T, et al: Epigenetic inactivation of Med Sci Monit 25: 3366‑3373, 2019. CHFR and sensitivity to microtubule inhibitors in gastric cancer. 52. Shen H, Zhang J, Zhang Y, Feng Q, Wang H, Li G, Jiang W Cancer Res 63: 8606‑8613, 2003. and Li X: Knockdown of tripartite motif 59 (TRIM59) inhibits 74. Kashima L, Idogawa M, Mita H, Shitashige M, Yamada T, proliferation in cholangiocarcinoma via the PI3K/AKT/mTOR Ogi K, Suzuki H, Toyota M, Ariga H, Sasaki Y and Tokino T: signaling pathway. Gene 698: 50‑60, 2019. CHFR protein regulates mitotic checkpoint by targeting PARP‑1 53. Chen G, Chen W, Ye M, Tan W and Jia B: TRIM59 knockdown protein for ubiquitination and degradation. J Biol Chem 287: inhibits cell proliferation by down‑regulating the Wnt/β‑catenin 12975‑12984, 2012. signaling pathway in neuroblastoma. Biosci Rep 39: pii: 75. Kim JH, Park SM, Kang MR, Oh SY, Lee TH, Muller MT and BSR20181277, 2019. Chung IK: Ubiquitin ligase MKRN1 modulates telomere length 54. Cui Z, Liu Z, Zeng J, Chen L, Wu Q, Mo J, Zhang G, Song L, homeostasis through a proteolysis of hTERT. Genes Dev 19: Xu W, Zhang S and Guo X: Eugenol inhibits non‑small cell lung 776‑781, 2005. cancer by repressing expression of NF‑κB‑regulated TRIM59. 76. Ko A, Shin JY, Seo J, Lee KD, Lee EW, Lee MS, Lee HW, Phytother Res 33: 1562‑1569, 2019. Choi IJ, Jeong JS, Chun KH and Song J: Acceleration of gastric 55. Halaby MJ, Hakem R and Hakem A: Pirh2: An E3 ligase tumorigenesis through MKRN1‑mediated posttranslational with central roles in the regulation of cell cycle, DNA damage regulation of p14ARF. J Natl Cancer Inst 104: 1660‑1672, 2012. response, and differentiation. Cell Cycle 12: 2733‑2737, 2013. 77. Jang JH: FIGC, a novel FGF‑induced ubiquitin‑protein ligase in 56. Bao Y, Wu X, Yuan D, Shi W and Shi J: High expression of gastric cancers FEBS Lett 578: 21‑25, 2004. Pirh2 is associated with poor prognosis in glioma. Cell Mol 78. Wu CE, Esfandiari A, Ho YH, Wang N, Mahdi AK, Neurobiol 37: 1501‑1509, 2017. Aptullahoglu E, Lovat P and Lunec J: Targeting negative regu‑ 57. Daks A, Petukhov A, Fedorova O, Shuvalov O, Merkulov V, lation of p53 by MDM2 and WIP1 as a therapeutic strategy in Vasileva E, Antonov A and Barlev NA: E3 ubiquitin ligase Pirh2 cutaneous melanoma. Br J Cancer 118: 495‑508, 2018. enhances tumorigenic properties of human non‑small cell lung 79. Hu C, Ni Z, Li BS, Yong X, Yang X, Zhang JW, Zhang D, Qin Y, carcinoma cells. Genes Cancer 7: 383‑393, 2016. Jie MM, Dong H, et al: hTERT promotes the invasion of gastric 58. Yang S, Chen Y, Sun F, Ni Q, Wang H, Huang Y, Zhang C, Liu K, cancer cells by enhancing FOXO3a ubiquitination and subse‑ Wang S, Qiu J, et al: Downregulated pirh2 can decrease the quent ITGB1 upregulation. Gut 66: 31‑42, 2017. proliferation of breast cancer cells. Arch Med Res 47: 186‑195, 80. Chi XZ, Kim J, Lee YH, Lee JW, Lee KS, Wee H, Kim WJ, 2016. Park WY, Oh BC, Stein GS, et al: Runt‑related transcription 59. Yang G, Gong Y, Wang Q, Wang L and Zhang X: miR‑100 antag‑ factor RUNX3 is a target of MDM2‑mediated ubiquitination. onism triggers apoptosis by inhibiting ubiquitination‑mediated Cancer Res 69: 8111‑8119, 2009. p53 degradation. Oncogene 36: 1023‑1037, 2017. 81. Jung CR, Lim JH, Choi Y, Kim DG, Kang KJ, Noh SM and Im DS: 60. Eichinger L, Pachebat JA, Glöckner G, Rajandream MA, Enigma negatively regulates p53 through MDM2 and promotes Sucgang R, Berriman M, Song J, Olsen R, Szafranski K, tumor cell survival in mice. J Clin Invest 120: 4493‑4506, Xu Q, et al: The genome of the social amoeba Dictyostelium 2010. discoideum. Nature 435: 43‑57, 2005. 82. Feng Y, Gao S, Gao Y, Song D, Wang X and Chen Z: Runx3 61. Langdon WY, Hyland CD, Grumont RJ and Morse HC III: The expression in rectal cancer cells and its effect on cell invasion c‑cbl proto‑oncogene is preferentially expressed in thymus and and proliferation. Oncol Lett 18: 3290‑3294, 2019. testis tissue and encodes a nuclear protein. J Virol 63: 5420‑5424, 83. Connell P, Ballinger CA, Jiang J, Wu Y, Thompson LJ, Höhfeld J 1989. and Patterson C: The co‑chaperone CHIP regulates protein 62. Lee H and Tsygankov AY: Cbl‑family proteins as regulators triage decisions mediated by heat‑shock proteins. Nat Cell Biol 3: of cytoskeleton‑dependent phenomena. J Cell Physiol 228: 93‑96, 2001. 2285‑2293, 2013. 84. Xiao M, Yan M, Zhang J, Xu Q and Chen W: Carboxy‑terminus 63. Kamei T, Machida K, Nimura Y, Senga T, Yamada I, Yoshii S, Hsc70 interacting protein exerts a tumor inhibition function in Matsuda S and Hamaguchi M: C‑Cbl protein in human cancer head and neck cancer. Oncol Rep 38: 1629‑1636, 2017. tissues is frequently tyrosine phosphorylated in a tumor‑specific 85. Liu F, Zhou J, Zhou P, Chen W and Guo F: The ubiquitin ligase manner. Int J Oncol 17: 335‑339, 2000. CHIP inactivates NF‑κB signaling and impairs the ability of 64. Dong Q, Liu YP, Qu XJ, Hou KZ and Li LL: Expression of c‑Cbl, migration and invasion in gastric cancer cells. Int J Oncol 46: Cbl‑b, and epidermal growth factor receptor in gastric carcinoma 2096‑2106, 2015. and their clinical significance. Chin J Cancer 29: 59‑64, 2010. 86. Zheng N, Schulman BA, Song L, Miller JJ, Jeffrey PD, Wang P, 65. Feng D, Ma Y, Liu J, Xu L, Zhang Y, Qu J, Liu Y and Qu X: Chu C, Koepp DM, Elledge SJ, Pagano M, et al: Structure of Cbl‑b enhances sensitivity to 5‑fluorouracil via EGFR‑ and the Cul1‑Rbx1‑Skp1‑F boxSkp2 SCF ubiquitin ligase complex. mitochondria‑mediated pathways in gastric cancer cells. Int J Nature 416: 703‑709, 2002. Mol Sci 14: 24399‑24411, 2013. 87. Lisztwan J, Marti A, Sutterlüty H, Gstaiger M, Wirbelauer C and 66. Yu P, Fan Y, Qu X, Zhang J, Song N, Liu J and Liu Y: Cbl‑b regu‑ Krek W: Association of human CUL‑1 and ubiquitin‑conjugating lates the sensitivity of cetuximab through ubiquitin‑proteasome enzyme CDC34 with the F‑box protein p45(SKP2): Evidence system in human gastric cancer cells. J BUON 21: 867‑873, for evolutionary conservation in the subunit composition of the 2016. CDC34‑SCF pathway. EMBO J 17: 368‑383, 1998. 67. CHe X, Zhang Y, Qu X, Guo T, Ma Y, Li C, Fan Y, Hou K, 88. Uddin S, Bhat AA, Krishnankutty R, Mir F, Kulinski M and Cai Y, Yu R, et al: The E3 ubiquitin ligase Cbl‑b inhibits tumor Mohammad RM: Involvement of F‑BOX proteins in progression growth in multidrug‑resistant gastric and breast cancer cells. and development of human malignancies. Semin Cancer Biol 36: Neoplasma 64: 887‑892, 2017. 18‑32, 2016. ONCOLOGY LETTERS 20: 22, 2020 11

89. Jiang ZH, Peng T, Qian HL, Lu CD, Qiu F and Zhang SZ: DNA 112. Bai J, Zhou Y, Chen G, Zeng J, Ding J, Tan Y, Zhou J and Li G: damage‑induced activation of ATM promotes β‑TRCP‑mediated Overexpression of Cullin1 is associated with poor prognosis of ARID1A ubiquitination and destruction in gastric cancer cells. patients with gastric cancer. Hum Pathol 42: 375‑383, 2011. Cancer Cell Int 19: 162, 2019. 113. Clifford SC, Cockman ME, Smallwood AC, Mole DR, 90. Milne AN, Leguit R, Corver WE, Morsink FH, Polak M, Woodward ER, Maxwell PH, Ratcliffe PJ and Maher ER: de Leng WW, Carvalho R and Offerhaus GJ: Loss of Contrasting effects on HIF‑1alpha regulation by disease‑causing CDC4/FBXW7 in gastric carcinoma. Cell Oncol 32: 347‑359, pVHL mutations correlate with patterns of tumourigenesis in 2010. von Hippel‑Lindau disease. Hum Mol Genet 10: 1029‑1038, 91. Li H, Wang Z, Zhang W, Qian K, Xu W and Zhang S: 2001. Fbxw7 regulates tumor apoptosis, growth arrest and the 114. Yokoe S, Nakagawa T, Kojima Y, Higuchi K and Asahi M: epithelial‑to‑mesenchymal transition in part through the RhoA Indomethacin‑induced intestinal epithelial cell damage is medi‑ signaling pathway in gastric cancer. Cancer Lett 370: 39‑55, ated by pVHL activation through the degradation of collagen 2016. I and HIF‑1α. Biochem Biophys Res Commun 468: 671‑676, 92. Huang LY, Zhao J, Chen H, Wan L, Inuzuka H, Guo J, Fu X, 2015. Zhai Y, Lu Z, Wang X, et al: SCFFBW7‑mediated degradation 115. Clifford SC, Astuti D, Hooper L, Maxwell PH, Ratcliffe PJ and of Brg1 suppresses gastric cancer metastasis. Nat Commun 9: Maher ER: The pVHL‑associated SCF ubiquitin ligase complex: 3569, 2018. molecular genetic analysis of elongin B and C, Rbx1 and 93. Kuai X, Li L, Chen R, Wang K, Chen M, Cui B, Zhang Y, HIF‑1alpha in renal cell carcinoma. Oncogene 20: 5067‑5074, Li J, Zhu H, Zhou H, et al: SCFFBXW7/GSK3β‑Mediated GFI1 2001. Degradation Suppresses Proliferation of Gastric Cancer Cells. 116. Gao L, Wu GJ, Liu B, Shen MZ, Pan TJ, Yu CG, Wang QH, Cancer Res 79: 4387‑4398, 2019. Ru Y, Liu XP, Niu TS, et al: Up‑regulation of pVHL along with 94. Zhou J, Hayakawa Y, Wang TC and Bass AJ: RhoA mutations down‑regulation of HIF‑1α by NDRG2 expression attenuates identified in diffuse gastric cancer. Cancer Cell 26: 9‑11, 2014. proliferation and invasion in renal cancer cells. PLoS One 8: 95. Gong J, Cui Z, Li L, Ma Q, Wang Q, Gao Y and Sun H: e84127, 2013. MicroRNA‑25 promotes gastric cancer proliferation, invasion, 117. Bowers AJ and Boylan JF: Nek8, a NIMA family kinase and migration by directly targeting F‑box and WD‑40 domain member, is overexpressed in primary human breast tumors. protein 7, FBXW7. Tumour Biol 36: 7831‑7840, 2015. Gene 328: 135‑142, 2004. 96. Lv Z, Zhang Y, Yu X, Lin Y and Ge Y: RETRACTED: The 118. Ding XF, Zhou J, Hu QY, Liu SC and Chen G: The tumor function of long non‑coding RNA MT1JP in the develop‑ suppressor pVHL down‑regulates never‑in‑mitosis A‑related ment and progression of gastric cancer. Pathol Res Pract 214: kinase 8 via hypoxia‑inducible factors to maintain cilia in 1218‑1223, 2018. human renal cancer cells. J Biol Chem 290: 1389‑1394, 2015. 97. Frescas D and Pagano M: Deregulated proteolysis by the F‑box 119. Ding XF, Chen J, Zhou J, Chen G and Wu YL: Never‑in‑mitosis proteins SKP2 and beta‑TrCP: Tipping the scales of cancer. A‑related kinase 8, a novel target of von‑Hippel‑Lindau tumor Nat Rev Cancer 8: 438‑449, 2008. suppressor protein, promotes gastric cancer cell proliferation. 98. Saitoh T and Katoh M: Expression profiles of betaTRCP1 and Oncol Lett 16: 5900‑5906, 2018. betaTRCP2, and mutation analysis of betaTRCP2 in gastric 120. Bianchi E, Denti S, Catena R, Rossetti G, Polo S, Gasparian S, cancer. Int J Oncol 18: 959‑964, 2001. Putignano S, Rogge L and Pardi R: Characterization of human 99. Gao G, Kun T, Sheng Y, Qian M, Kong F, Liu X, Yu Z, Zhang H, constitutive photomorphogenesis protein 1, a RING finger Zhang Q, Gu J and Zhang X: SGT1 regulates Akt signaling by ubiquitin ligase that interacts with Jun transcription factors promoting beta‑TrCP‑dependent PHLPP1 degradation in gastric and modulates their transcriptional activity. J Biol Chem 278: cancer cells. Mol Biol Rep 40: 2947‑2953, 2013. 19682‑19690, 2003. 100. Wang S, Zhang Y, Wang Y, Ye P, Li J, Li H, Ding Q and Xia J: 121. Zhu D, Maier A, Lee JH, Laubinger S, Saijo Y, Wang H, Qu LJ, Amphiregulin confers regulatory T cell suppressive function Hoecker U and Deng XW: Biochemical characterization of and tumor invasion via the EGFR/GSK‑3β/Foxp3 axis. J Biol Arabidopsis complexes containing CONSTITUTIVELY Chem 291: 21085‑21095, 2016. PHOTOMORPHOGENIC1 and SUPPRESSOR OF PHYA 101. Li LQ, Pan D, Chen H, Zhang L and Xie WJ: F‑box protein proteins in light control of plant development. Plant Cell 20: FBXL2 inhibits gastric cancer proliferation by ubiquitin‑mediated 2307‑2323, 2008. degradation of forkhead box M1. FEBS Lett 590: 445‑452, 2016. 122. Saijo Y, Zhu D, Li J, Rubio V, Zhou Z, Shen Y, Hoecker U, 102. Cen G, Ding HH, Liu B and Wu WD: FBXL5 targets cortactin Wang H and Deng XW: Arabidopsis COP1/SPA1 complex for ubiquitination‑mediated destruction to regulate gastric and FHY1/FHY3 associate with distinct phosphorylated forms cancer cell migration. Tumour Biol 35: 8633‑8638, 2014. of phytochrome A in balancing light signaling. Mol Cell 31: 103. Wu W, Ding H, Cao J and Zhang W: FBXL5 inhibits metas‑ 607‑613, 2008. tasis of gastric cancer through suppressing Snail1. Cell Physiol 123. Ka WH, Cho SK, Chun BN, Byun SY and Ahn JC: The ubiquitin Biochem 35: 1764‑1772, 2015. ligase COP1 regulates cell cycle and apoptosis by affecting p53 104. Zou S, Ma C, Yang F, Xu X, Jia J and Liu Z: FBXO31 Suppresses function in human breast cancer cell lines. Breast Cancer 25: gastric cancer EMT by targeting Snail1 for proteasomal degra‑ 529‑538, 2018. dation. Mol Cancer Res 16: 286‑295, 2018. 124. Zou S, Zhu Y, Wang B, Qian F, Zhang X, Wang L, Fu C, Bao H, 105. Petroski MD and Deshaies RJ: Function and regulation of Xie M, Gao S, et al: The ubiquitin ligase COP1 promotes glioma cullin‑RING ubiquitin ligases. Nat Rev Mol Cell Biol 6: 9‑20, cell proliferation by preferentially downregulating tumor 2005. suppressor p53. Mol Neurobiol 54: 5008‑5016, 2017. 106. Morimoto M, Nishida T, Honda R and Yasuda H: Modification 125. Li YF, Wang DD, Zhao BW, Wang W, Huang CY, Chen YM, of cullin‑1 by ubiquitin‑like protein Nedd8 enhances the Zheng Y, Keshari RP, Xia JC and Zhou ZW: High level of COP1 activity of SCF(skp2) toward p27(kip1). Biochem Biophys Res expression is associated with poor prognosis in primary gastric Commun 270: 1093‑1096, 2000. cancer. Int J Biol Sci 8: 1168‑1177, 2012. 107. Cheng Q and Yin G: Cullin‑1 regulates MG63 cell proliferation 126. Sawada G, Ueo H, Matsumura T, Uchi R, Ishibashi M, Mima K, and metastasis and is a novel prognostic marker of osteosar‑ Kurashige J, Takahashi Y, Akiyoshi S, Sudo T, et al: Loss of coma. Int J Biol Markers 32: e202‑e209, 2017. COP1 expression determines poor prognosis in patients with 108. Zhou YH, Xia J, Xu WH, Zhu X, Wu XH, Hua D and Xing C: gastric cancer. Oncol Rep 30: 1971‑1975, 2013. Cullin‑1 promotes cell proliferation in human breast cancer and 127. Rotin D and Kumar S: Physiological functions of the HECT is related to diabetes. Int J Biol Markers 31: e375‑e381, 2016. family of ubiquitin ligases. Nat Rev Mol Cell Biol 10: 398‑409, 109. Jiang H, He D, Xu H, Liu J, Qu L and Tong S: Cullin‑1 promotes 2009. cell proliferation via cell cycle regulation and is a novel in pros‑ 128. Zheng H, Ke X, Li D, Wang Q, Wang J, Liu X, Deng M, Deng X, tate cancer. Int J Clin Exp Pathol 8: 1575‑1583, 2015. Xue Y, Zhu Y and Wang Q: NEDD4 promotes cell growth and 110. Chen TJ, Gao F, Yang T, Thakur A, Ren H, Li Y, Zhang S, motility in hepatocellular carcinoma. Cell Cycle 17: 728‑738, 2018. Wang T and Chen MW: CDK‑associated Cullin 1 promotes cell 129. Shao G, Wang R, Sun A, Wei J, Peng K, Dai Q, Yang W and proliferation with activation of ERK1/2 in human lung cancer Lin Q: The E3 ubiquitin ligase NEDD4 mediates cell migration A549 cells. Biochem Biophys Res Commun 437: 108‑113, 2013. signaling of EGFR in lung cancer cells. Mol Cancer 17: 24, 2018. 111. Michail O, Moris D, Theocharis S and Griniatsos J: Cullin‑1 130. Kim SS, Yoo NJ, Jeong EG, Kim MS and Lee SH: Expression and ‑2 protein expression in colorectal cancer: Correlation with of NEDD4‑1, a PTEN regulator, in gastric and colorectal carci‑ clinicopathological variables. In Vivo 32: 391‑396, 2018. nomas. APMIS 116: 779‑784, 2008. 12 WANG et al: E3 UBIQUITIN LIGASES IN GASTRIC CANCER

131. Zou X, Levy‑Cohen G and Blank M: Molecular functions of 146. Vassilev LT, Vu BT, Graves B, Carvajal D, Podlaski F, NEDD4 E3 ubiquitin ligases in cancer. Biochim Biophys Filipovic Z, Kong N, Kammlott U, Lukacs C, Klein C, et al: Acta 1856: 91‑106, 2015. In vivo activation of the p53 pathway by small‑molecule antago‑ 132. Zhang L, Wu Z, Ma Z, Liu H, Wu Y and Zhang Q: WWP1 as a nists of MDM2. Science 303: 844‑848, 2004. potential tumor oncogene regulates PTEN‑Akt signaling pathway 147. Impicciatore G, Sancilio S, Miscia S and Di Pietro R: Nutlins in human gastric carcinoma. Tumour Biol 36: 787‑798, 2015. and ionizing radiation in cancer therapy. Curr Pharm Des 16: 133. Ma L, Chen X, Li C, Cheng R, Gao Z, Meng X, Sun C, Liang C 1427‑1442, 2010. and Liu Y: miR‑129‑5p and ‑3p co‑target WWP1 to suppress 148. Yee‑Lin V, Pooi‑Fong W and Soo‑Beng AK: Nutlin‑3, A gastric cancer proliferation and migration. J Cell Biochem, Nov p53‑Mdm2 antagonist for nasopharyngeal carcinoma treatment. 11, 2018 (Epub ahead of print). Mini Rev Med Chem 18: 173‑183, 2018. 134. Li Q, Li Z, Wei S, Wang W, Chen Z, Zhang L, Chen L, Li B, Sun G, 149. Meijer A, Kruyt FA, van der Zee AG, Hollema H, Le P, ten Xu J, et al: Overexpression of miR‑584‑5p inhibits proliferation Hoor KA, Groothuis GM, Quax WJ, de Vries EG and de Jong S: and induces apoptosis by targeting WW domain‑containing E3 Nutlin‑3 preferentially sensitises wild‑type p53‑expressing ubiquitin protein ligase 1 in gastric cancer. J Exp Clin Cancer cancer cells to DR5‑selective TRAIL over rhTRAIL. Br J Res 36: 59, 2017. Cancer 109: 2685‑2695, 2013. 135. Zhu H, Kavsak P, Abdollah S, Wrana JL and Thomsen GH: A 150. Lee DM, Kim IY, Seo MJ, Kwon MR and Choi KS: Nutlin‑3 SMAD ubiquitin ligase targets the BMP pathway and affects enhances the bortezomib sensitivity of p53‑defective cancer embryonic pattern formation. Nature 400: 687‑693, 1999. cells by inducing paraptosis. Exp Mol Med 49: e365, 2017. 136. Koganti P, Levy‑Cohen G and Blank M: Smurfs in protein 151. Endo S, Yamato K, Hirai S, Moriwaki T, Fukuda K, Suzuki H, homeostasis, signaling, and cancer. Front Oncol 8: 295, 2018. Abei M, Nakagawa I and Hyodo I: Potent in vitro and in vivo 137. Dote H, Toyooka S, Tsukuda K, Yano M, Ota T, Murakami M, antitumor effects of MDM2 inhibitor nutlin‑3 in gastric cancer Naito M, Toyota M, Gazdar AF and Shimizu N: Aberrant cells. Cancer Sci 102: 605‑613, 2011. promoter methylation in human DAB2 interactive protein 152. Wei YS and Adachi I: Inhibitory effect of triptolide on colony (hDAB2IP) gene in gastrointestinal tumour. Br J Cancer 92: formation of breast and stomach cancer cell lines. Zhongguo 1117‑1125, 2005. Yao Li Xue Bao 12: 406‑410, 1991. 138. Li X, Dai X, Wan L, Inuzuka H, Sun L and North BJ: Smurf1 153. Jiang XH, Wong BC, Lin MC, Zhu GH, Kung HF, Jiang SH, regulation of DAB2IP controls cell proliferation and migration. Yang D and Lam SK: Functional p53 is required for trip‑ Oncotarget 7: 26057‑26069, 2016. tolide‑induced apoptosis and AP‑1 and nuclear factor‑kappaB 139. Tao Y, Sun C, Zhang T and Song Y: SMURF1 promotes the activation in gastric cancer cells. Oncogene 20: 8009‑8018, proliferation, migration and invasion of gastric cancer cells. 2001. Oncol Rep 38: 1806‑1814, 2017. 154. Wang BY, Cao J, Chen JW and Liu QY: Triptolide induces apop‑ 140. Yang M, Jiang N, Cao QW, Ma MQ and Sun Q: The E3 ligase tosis of gastric cancer cells via inhibiting the overexpression of UBR5 regulates gastric cancer cell growth by destabilizing the MDM2. Med Oncol 31: 270, 2014. tumor suppressor GKN1. Biochem Biophys Res Commun 478: 155. Choi HS, Seo HS, Kim JH, Um JY, Shin YC and Ko SG: Ethanol 1624‑1629, 2016. extract of paeonia suffruticosa Andrews (PSE) induced AGS 141. Kozlov G, Nguyen L, Lin T and De Crescenzo G, Park M and human gastric cancer cell apoptosis via fas‑dependent apoptosis Gehring K: Structural basis of ubiquitin recognition by the and MDM2‑p53 pathways. J Biomed Sci 19: 82, 2012. ubiquitin‑associated (UBA) domain of the ubiquitin ligase EDD. 156. Lan H, Tang Z, Jin H and Sun Y: Neddylation inhibitor J Biol Chem 282: 35787‑35795, 2007. MLN4924 suppresses growth and migration of human gastric 142. Kim MS, Oh JE, Eom HS, Yoo NJ and Lee SH: Mutational cancer cells. Sci Rep 6: 24218, 2016. analysis of UBR5 gene encoding an E3 ubiquitin ligase in 157. Eto K, Iwatsuki M, Watanabe M, Ishimoto T, Ida S, Imamura Y, common human cancers. Pathology 42: 93‑94, 2010. Iwagami S, Baba Y, Sakamoto Y, Miyamoto Y, et al: The 143. Richardson PG, Hideshima T and Anderson KC: Bortezomib sensitivity of gastric cancer to trastuzumab is regulated by (PS‑341): A novel, first‑in‑class proteasome inhibitor for the the miR‑223/FBXW7 pathway. Int J Cancer 136: 1537‑1545, treatment of multiple myeloma and other cancers. Cancer 2015. Control 10: 361‑369, 2003. 158. Schneekloth JS Jr and Crews CM: Natural product inhibitors 144. Zhang B and Gu Y: Bortezomib inhibits gastric carcinoma of the ubiquitin‑proteasome pathway. Curr Drug Targets 12: HGC‑27 cells through the phospho‑Jun N‑terminal kinase 1581‑1594, 2011. (p‑JNK) pathway in vitro. Gene 559: 164‑171, 2015. 145. Yi H, Yan X, Luo Q, Yuan L, Li B, Pan W, Zhang L, Chen H, This work is licensed under a Creative Commons Wang J, Zhang Y, et al: A novel small molecule inhibitor of Attribution-NonCommercial-NoDerivatives 4.0 MDM2‑p53 (APG‑115) enhances radiosensitivity of gastric International (CC BY-NC-ND 4.0) License. adenocarcinoma. J Exp Clin Cancer Res 37: 97, 2018.